Herein we describe inhibitors of aldosterone synthase that have the potential to protect from organ/tissue damage caused by an absolute or relative excess of aldosterone. Hypertension affects about 20% of the adult population in developed countries. In persons 60 years and older, this percentage increases to above 60%. Hypertensive subjects display an increased risk of other physiological complications including stroke, myocardial infarction, atrial fibrillation, heart failure, peripheral vascular disease and renal impairment. The renin angiotensin aldosterone system is a pathway that has been linked to hypertension, volume and salt balance and more recently to contribute directly to end organ damage in advanced stages of heart failure or kidney disease. ACE inhibitors and angiotensin receptor blockers (ARBs) are successfully used to improve duration and quality of life of patients. These drugs are not yielding maximum protection. In a relatively large number of patients ACE and ARB's lead to so-called aldosterone breakthrough, a phenomenon where aldosterone levels, after a first initial decline, return to pathological levels. It has been demonstrated that the deleterious consequences of inappropriately increased aldosterone levels (in relation to salt intake/levels) can be minimized by aldosterone blockade with mineralocorticoid receptor antagonists. A direct inhibition of aldosterone synthesis is expected to provide even better protection as it will also reduce non-genomic effects of aldosterone as well.
The effects of aldosterone on Na/K transport lead to increased re-absorption of sodium and water and the secretion of potassium in the kidneys. Overall this results in increased blood volume and, therefore, increased blood pressure. Beyond its role in the regulation of renal sodium re-absorption aldosterone can exert deleterious effects on the kidney, the heart and the vascular system especially in a “high sodium” context. It has been shown that under such conditions aldosterone leads to increased oxidative stress which ultimately may contribute to organ damage. Infusion of aldosterone into renally compromised rats (either by high salt treatment or by unilaterally nephrectomy) induces a wide array of injuries to the kidney including glomerular expansion, podocyte injury, interstitial inflammation, mesangial cell proliferation and fibrosis reflected by proteinuria. More specifically aldosterone was shown to increase the expression of the adhesion molecule ICAM-1 in the kidney. ICAM-1 is critically involved in glomerular inflammation. Similarly, aldosterone was shown to increase the expression of inflammatory cytokines, such as interleukin IL-1b and IL-6, MCP-1 and osteopontin. On a cellular level it was demonstrated that in vascular fibroblasts aldosterone increased the expression of type I collagen mRNA, a mediator of fibrosis. Aldosterone also stimulates type IV collagen accumulation in rat mesangial cells and induces plasminogen activator inhibitor-1 (PAI-1) expression in smooth muscle cells. In summary aldosterone has emerged as a key hormone involved in renal damage. Aldosterone plays an equally important role in mediating cardiovascular risk.
There is ample preclinical evidence that MR-antagonists (spironolactone and eplerenone) improve blood pressure, cardiac and renal function in various pre-clinical models.
More recently preclinical studies highlight the important contribution of CYP11B2 to cardiovascular and renal morbidity and mortality. The CYP11B2 inhibitor FAD286 and the MR antagonist spironolactone were evaluated in a rat model of chronic kidney disease (high angiotensin II exposure; high salt and uni-nephrectomy). Angiotensin II and high salt treatment caused albuminuria, azotemia, renovascular hypertrophy, glomerular injury, increased PAI-1, and osteopontin mRNA expression, as well as tubulointerstitial fibrosis. Both drugs prevented these renal effects and attenuated cardiac and aortic medial hypertrophy. Following 4 weeks of treatment with FAD286, plasma aldosterone was reduced, whereas spironolactone increased aldosterone at 4 and 8 weeks of treatment. Similarly only spironolactone but not FAD286 enhanced angiotensin II and salt-stimulated PAI-1 mRNA expression in the aorta and the heart. In other studies the CYP11B2 inhibitor FAD286 improved blood pressure and cardiovascular function and structure in rats with experimental heart failure. In the same studies FAD286 was shown to improve kidney function and morphology.
Administration of an orally active CYP11B2 inhibitor, LCI699, to patients with primary aldosteronism, lead to the conclusion that it effectively inhibits CYP11B2 in patients with primary aldosteronism resulting in significantly lower circulating aldosterone levels and that it corrected the hypokalemia and mildly decreased blood pressure. The effects on the glucocorticoid axis were consistent with a poor selectivity of the compound and a latent inhibition of cortisol synthesis. Taken together these data support the concept that a CYP11B2 inhibitor can lower inappropriately high aldosterone levels. Achieving good selectivity against CYP11B1 is important to be free of undesired side effects on the HPA axis and will differentiate different CYP11B2 inhibitors.